Elongated inflatable parabolic antenna



Nov. 26, 1968 R. J. KOEHLER 3,413,645

ELONGATED INFLATABLE PARABOLIC ANTENNA Filed April 7. 1966 I87 24 lo INVENTOR RICHARD J. KOEHLER BY ATTORNEY United States Patent 3,413,645 ELONGATED INFLATABLE PARABOLIC ANTENNA Richard J. Koehler, Ellicott City, Md., assignor, by mesne assignments, to the United States of America, as represented by the Secretary of the Navy Filed Apr. 7, 1966, Ser. No. 541,034 5 Claims. (Cl. 343-872) This invention relates to radar antenna systems and more particularly to an inflatable antenna arrangement which is of light weight construction and readily mobile.

There are several types of inflatable or collapsible antenna arrangements in the prior art for use in ground installations or for use in airborne installations. The prior art inflatable or collapsible antennas are designed to provide an envelope which assumes, when inflated, a shape which may range from a spherical shape to an oblate shape. In such structures the antenna reflector may be a surface which is formed of a metallic coating located on an inner face of the inflatable envelope, or it may be formed of a membrane or a diaphragm structure which is fixedly located on or within the inflated envelope.

The prior art inflatable supports have been found to present difliculties in use due to their ready deformability under stresses, unless they are strengthened by cumbersome reinforcements. For example, the more frequent problem resides in the tendency of the inflated envelope to become distorted due to wind and other factors which results in some distortion of the antenna reflecting surface. Another disadvantage results from their use in extrerne low temperature which causes deformation in the shape of the envelope by ice formation and consequent distortion of the reflecting surface.

An object of the present invention is to provide an inflatable parabolic antenna having an optimum configuration and which is generally unaffected by weight and wind stresses or loads.

Another object of the invention is to provide an inflatable type antenna having a parabolic configuration and which is designed for different vertical and horizontal beam widths.

The invention contemplates an inflatable antenna which includes a membrane or diaphragm reflector which is formed of a particular shape and fixedly located within an inflatable envelope in spaced relation with the opposed side walls of the envelope. The membrane or diaphragm reflector is developed from a paraboloid of revolution to provide a smaller aperture in one plane and a larger aperture in the plane perpendicular thereto. The smaller aperture is formed by truncating a paraboloid of revolution with two parallel horizontal planes and the larger horizontal aperture is defined by the closed ends of the envelope within which the reflector is located. The inflatable envelope which receives the reflector is preferably in the form of toroid having a length and width which is commensurate with or determined by the configuration of the reflector. The materials for forming the inflatable antenna will be selected for optimum properties, for example, the envelope may be constructed of a tough relatively low modulus flexible material while the reflector may be constructed of a relatively high modulus flexible material. Specifically, stretch resistant vinyl-coated fiberglass may be used to construct these elements of the inflatable antenna.

FIGURE 1 is a view in general elevation showing the inflated antenna device supported on a base and partially sectioned to show a detail. 1

FIGURE 2 is a view in horizontal section of the antenna device of FIGURE 1.

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FIGURE 3 is a view in vertical section of the antenna device of FIGURE 1.

In the drawings, the envelope depicted in inflated state, is indicated at 10 and may be considered as a support or mounting for the antenna reflector. In FIGURE 1, the envelope 10 is mounted for movement horizontally on support structure 12 which is shown in phantom lines as representative of any selected structure which permits the envelope 10 to be rotated. The envelope 10, as shown in FIGURE 2, is toroidal and closed by similar spherical or ellipsoidal end caps 14 and 16. The reflector is indicated at 18, is parabolic in shape, as seen in FIGURES 2 and 3, and is located generally centrally or axial-1y of the envelope 10 and forms opposed chambers 20 and 22 on either side as indicated. It will beunderstood that the reflector 18 is fixed to the material forming the envelope 10 in some suitable manner, depending on the materials used and forms a partition for the envelope.

FIGURE 1 is cut away to show a portion of the reflector 18 which will be understood to have a shape 'and such dimensions as to be coter minus with the outline of the envelope as shown in FIGURE 1. That is, the reflector 16 which is formed as heretofore described will have a small vertical dimension V and a larger horizontal dimension H as shown in FIGURE 1 providing for different vertical and horizontal apertures to adapt the device to radar designs which require different vertical and horizontal beam widths.

The above described inflatable antenna has numerous advantages. For example, the actual size of the envelope of the assembly is limited by the dimensions of the antenna aperture of reflector 18 with the resultant advantage that minimum weight and wind loads only are required for the support structure for the assembly. Also, the assembly permits much higher absolute pressures to be used and consequently affords greater wind resistance. In this connection a vertical strut means 24, for example, of fiberglass may extend transversely of the envelope generally parallel with the reflector 18, as shown in FIGURE 1, to limit deflection. And additionally, rotation of the assembly will require minimum power requirements because of its low profile and aerodynamic shape.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1. A radar antenna assembly comprising,

(a) an elongate inflatable envelope,

(b) a reflective diaphragm within said envelope and extending axially thereof and (c) said diaphragm being parabolic in shape and providing a small wave energy aperture in one plane and and a relatively larger wave energy aperture in the plane perpendicular thereto.

'2. A radar antenna assembly as in claim 1, further characterized by,

(a) the elongate inflatable envelope being in the shape of a toroid and formed of stretch resistant flexible material.

3. A radar antenna assembly as in claim 1, further characterized by,

(a) the reflective diaphragm having substantial rigidity and providing a partition dividing the envelope into opposed compartments.

4. A radar antenna assembly as in claim 1, further characterized by,

A J .1: (a) the reflective diaphragm having the configuration References Cited of a section severed from a paraboloid of revolution by two parallel planes. UNITED STATES PATENTS 5. A radar antenna assembly as in claim 1, further 2,814,038 11/1957 Miller 343-915 characterized by, 5 3,221,333 11/1965 Brown 3439l5 (a) strut means extending transversely of the envelope in generally parallel relation with the reflector. ELI LIEBERMAN, Primary Examiner. 

1. A RADAR ANTENNA ASSEMBLY COMPRISING, (A) AN ELONGATE INFLATABLE ENVELOPE, (B) A REFLECTIVE DIAPHRAGM WITHIN SAID ENVELOPE AND EXTENDING AXIALLY THEREOF AND (C) SAID DIAPHRAGM BEING PARABOLIC IN SHAPE AND PROVIDING A SMALL WAVE ENERGY APERTURE IN ONE PLANE 